Atomizer wheel for the atomization of suspensions of hard-wearing materials



K. NIELSE 3,454,226 M WHEEL FOR THE MIZATION OF SP 0N5 0F HARD-WEARINGMATERIALS Filed March 22. 1966 ATO SU July 8, 1969 INVENTOR v ATTORNEYS19/ 27/ FIG.3

FIGA W:

United States Patent 6 Int. Cl. Bb 3/10; F23d 11/08; B04b 11/00 U.S. Cl.239-224 7 Claims ABSTRACT OF THE DISCLOSURE An atomizer wheel comprisingan annular chamber provided with a number of conical outlet holes linedwith bushings extending a distance into the chamber.

This invention relates to an atomizer wheel for the atomization ofsuspensions of hard-wearing materials and of the type whichconcentrically with the hub of the wheel has an annular bowl-shapedspace in the substantially cylindrical outer wall of which there areprovided a plurality of discharge openings having linings of awear-resistant sintered material.

In this case sintered materia means a material where the hard grains arestably interconnected no matter whether such interconnection has beeneffected by fusing together the surfaces of the grains or by embeddingthe grains in some basic substance such as, by Way of example, is beingused in the manufacture of Wolfram carbide bodies.

In the atomization of suspensions which contain solid particles of ahard material, especially sharp edged par-.

ticles, for example a suspension of ceramic clay, a very hard wear istaking place on account of the very high velocities of discharge fromthe atomizer wheel caused by the centrifugal force. Thus, a conventionalatomizer wheel made of the commonly used wear-resistant types of steel,will have an extremely short lifetime, sometimes only a few hours oreven less before they have become so heavily worn as to be entirelyunserviceable.

With a view to reducing the wear it is known to employ wear-resistantsintered materials in such places where the wear occurs.

On account of their hardness such sintered materials are practicallyspeaking not machinable so that the wearresistant parts to be used mustbe produced in their final shape by sintering which in conjunction withthe circumstance that they do in all essentials only withstandcompressive forces and must not, on account of their brittleness, beexposed to tensile or bending stresses of significance, has the effectthat they only lend themselves to be produced in very simple geometricshapes.

There is known an atomizer wheel of the type concerned having slotdischarge openings where plates of such sintered material are insertedinto the slot openings at the walls thereof across which the dischargeis taking place. The plates are loosely disposed for the very reason ofavoiding bending stresses and are retained by their end edges engaging aprojecting edge provided at the external opening of the slot, againstwhich latter edge they are firmly pressed by the centrifugal forceduring rotation of the wheel. This measure prolongs the lifetime of thewheel to some extent but it proves in practice that this is neverthelessonly a rather limited improvement in that the liquid is by thecentrifugal force pressed in between the loosely deposited plates andthe adjoining surface of the wheel proper whereby the material of thewheel is quickly worn to such extent as to make the wheel discardable.

Instead of the slot openings one has tried to use cylindrical holes inwhich there are disposed bushings of a wear-resistant sintered materialbut in this case it proves that the outer wall of the wheel is worn inthe area surrounding the bushings so that the wheel is discardable aftera few hours of operation so that practically no improvement is obtainedby using the wear-resistant bushmgs.

The invention has for its object to provide an atomizer wheel of thetype concerned in connection with which a very considerable increase ofthe lifetime is obtained.

One object of the invention is to provide the holes with linings oftapered bushings of wear-resistant sintered material, projecting intothe bowl-shaped space.

As a consequence of the tapered shape of the bushings they are duringoperation of the wheel pressed firmly against the correspondingly shapedwall surfaces of the openings by the centrifugal force so that anydischarge of liquid between the bushings and the material of the wheelproper is avoided. As the bushings extend a distance into the annularspace in the wheel, a layer of liquid will deposit on the outer wallduring the rotation of the wheel. Owing to the centrifugal forces theheavier parts of the layer i.e. the suspended solid material isseparated from the liquid in the layer and deposited directly on thewall so as to fill the area surrounding the inwardly extending portionsof the bushings. The coating thus obtained is, to be sure, notwear-resistant in the proper sense of the word in that it consists ofloosely interconnected particles which are incessantly torn way from thesurface of the layer by the suspension flowing towards the openings ofthe bushings but the centrifugation of particles out into said layerwill continuously have the effect that the torn-away particles arereplaced by fresh particles so that the parts of the coating adjoiningthe wall are preserved and preclude any wear of said wall. In practiceit proves that in this way lifetime can increase several hundred times.

Although the bushings consist of the said wear-resistant sinteredmaterial, they will nevertheless be subject to wear but they are readilyreplaceable because they are only kept in place by the centrifugal forcewhich, as a matter of fact, is inoperative when the wheel is at rest.The wear to which the bushings are exposed is unilateral and theirlifetime may, therefore, be increased by turning them gradually as theyare worn.

The openings of the bushings may by way of example have a circular crosssection but preferably they are of a square cross section. The squarecross section determines four different well-defined positions of thebushings. Further the wearing surfaces are plane which has proved toinvolve a longer lifetime than curved wearing surfaces.

A wearing groove may be produced in the annular space at the place wherethe surface of said coating adjoins the bottom of the wheel. This wearmay be essentially reduced when the bottom of the bowl-shaped space hasa conical shape sloping outwardly towards the outer wall.

In a particular embodiment of the atomizer wheel according to theinvention a layer of a wear-resistant material is provided on the bottomsurface of the bowlshaped space made for either in the shape of anembedded annular plate or a sintered surface coating at any rate in theoutermost part of the bottom surface. In this place the wear may be lesshard than in the bushings proper and through a surface coating ofwear-resistant material it is possible to obtain the advantage that thelifetime of the wheel proper becomes of a length sufficient forpermitting the bushings being replaced a number of times before thewheel is discardable. If using an embedded ring this ring can also bereplaced and, consequently, the longest imaginable lifetime of the wheelis attained.

Sometimes it may be difficult or at any rate expensive to produce thesaid annular plate of sintered material, but excellent results are alsoobtained by using a ring of a wear-resistant metal alloy because thewear at this place is, as mentioned above, less hard than in thedischarge openings.

The invention will be particularly explained below with reference to theaccompanying drawings.

FIG. 1 shows a sectional view an embodiment of the atomizer wheelaccording to the invention.

FIG. 2 the same atomizer wheel as seen from the supply side.

FIG. 3 shows a modified embodiment of the atomizer wheel in a sectionalview.

FIG. 4 a modification of a part of the atomizer wheel shown in FIG. 1 or3.

The wheel illustrated in FIG. 1 is substantially of bowlshape with acentrally disposed hub 1 whereby an annular space 2 appears between thehub 1 and the outer wall 3 of the wheel which space is further definedby the wheel portion 4 connecting the hub 1 with the outer wall 3 andforming the bottom of the annular space 2. Further, an annular coverplate 5 is secured to the upper side of the wheel, said cover platesurrounding the hub 1 in such a manner as to form between said hub andthe annular plate 5 an annular opening 6 leading into the space 2.

The wheel is intended for being mounted into a known spray-dryingapparatus on a shaft which during operation rotates at a very highvelocity, a suspension being supplied to the space through the opening 6and precipitated in atomized form through openings in the side wall 3 toa surrounding drying chamber wherein the fine particles formed by theatomization are dried so that their contents of solid matter fall to thebottom of the drying chamber in the form of a fine powder.

FIGS. 1 and 2 show a single one of said openings, and according to theinvention a bushing 7 of a wearresistant sintered material, for exampleWolfram carbide, silicon carbide, aluminium oxide or tetraboron carbide,is disposed in each of said openings.

These bushings 7 have conical outer surfaces with outwardly decreasingdiameter and, consequently, they can be loosely disposed in saidopenings as they are pressed outwardly by the centrifugal force when theWheel is rotated and, consequently, they are immovably andtightfittingly secured in the openings in the outer wall.

At their outer ends the bushings 7 are preferably ground flush with thecylindrical outer surface of the wheel whilst their inwardly facing endsextend a distance into the space 2 beyond the outer wall 3 as seen inFIG. 1.

When the wheel commences to rotate the surroundings of the bushingsadjoining the outer wall will very quickly be filled with a layer of thesuspension as a consequence of the effect of the centrifugal force, asindicated by a dotted line 8. By the centrifuging effect the material ofthis layer is quickly separated so that the heavier parts, i.e. thecontents of solid wearing particles will adopt the outer position closedto the outer wall 3, whilst the lighter parts, i.e. the liquid will lieinnermost. In this manner the surroundings of the bushings 7 are quicklyfilled with a layer of these solid particles which will thus protect thematerial of the wheel proper from wear.

A certain Wearing effect may occur at the bottom of the space 2 andprimarily at the vicinity of the bordering line 8 for the materialdeposited on the outer wall 3. For the purpose of preventing the wheelfrom being quickly ruined by this wearing effect, an annular plate 9 ofa wear-resistant material is embedded at the bottom of the space. Ifdeemed appropriate, this material may likewise be a hard sinteredmaterial but since this area is subject to somewhat less wear it willoften suffice to use a wear-resistant metal alloy, for example awearresistant type of steel.

The embodiment shown in FIG. 3 differs from that shown in FIG. 1 in thatinstead of the annular plate 9 a layer 10 of a wear-resistant materialhas been applied to the bottom of the space 2, said layer extending adistance upwardly along the hub 1. Since the said layer is notreplaceable in the same manner as that used in FIG. 1, it may beexpedient that said layer consists of a wearresistant sintered material.

FIG. 4 shows a modified embodiment of the bushings having squarecross-section instead of circular crosssection as shown in FIGS. 1 and3. The bushings are tapered at least over part of its length 11corresponding to the conical part of the bushings 7 in FIGS. 1 and 3.

The bottom of the annular space may be conically sloping outwards fromthe hub 1 as indicated in FIG. 1 by means of a dotted line 12.

I claim:

1. An atomizer wheel comprising a hub, an outer wall part coaxiallydisposed about said hub and a bottom part connecting said outer wallpart with said hub, said outer wall part, said hub, and said bottom partdefining between them an annular chamber, a ring-shaped cover memberdetachably connected to said outer Wall part, said cover member havingan inner circumference defining together with said hub an unobstructedspace in communication with said annular chamber, said outer wall partbeing provided with a plurality of regularly shaped holes uniformlydistributed around the circumference of the outer wall part, said holesforming the only outlet openings of the wheel, each of said holes beinglined with bushing of wear-resistant sintered material, said holes andsaid bushings being tapered in direction radially outwardly from saidchamber, the inner end of each of said bushings projecting into saidchamber while their outer ends are substantially flush with the outsideof said outer wall part.

2. An atomizer wheel as claimed in claim 1, wherein said bushings havecircular cross-sections.

3. An atomizer wheel as claimed in claim 1, wherein said bushings havesquare shaped cross-sections.

4. An atomizer wheel as claimed in claim 1, wherein a plate ofwear-resistant material is embedded in the surface of said bottom part,facing said annular chamber.

5. An atomizer wheel as claimed in claim 1, wherein said bottom part hasa sintered wear-resistant surface coating facing said annular chamber.

6. An atomizer wheel as claimed in claim 1, wherein said bottom part hasa conical surface sloping outwards from said hub within said annularchamber.

7. An atomizer wheel comprising a hub, an outer wall member coaxiallydisposed about said hub, a bottom member connecting said outer wallmember with said hub, the upper surface of said bottom member being of awear-resistant material, said outer wall member, said hub, and saidbottom member defining between them an annular chamber, a ring-shapedcover member detachably connected to said outer wall member, said covermember having an inner circumference defining, together with said hub,an inlet opening in communication with said annular chamber, said outerwall member being provided with a plurality of uniform outlet openingsuniformly distributed about the periphery of the outer wall part andforming 5 6 the only outlet openings of said wheel, and a bushing of2,695,748 11/1954 Millard 23347 wear-resistant sintered materialextending radially through 3,079,069 2/ 1963' Thylefors 23 3-46 X R eachopening and projecting into said chamber, said holes 3,094,487 6/1963Van Arsdell 23346 XR and said bushings being tapered in a directionradially 3,108,952 10/1963 Antz 23314 outward from said chamber. 53,228,598 1/ 1966 Keith 23347 XR References Cited HENRY T. KLINKSIEK,Primary Examiner.

UNITED STATES PATENTS US. Cl. X R

2,645,415 7/1953 Strezynski 23328 23347

